Requite (6)
I believe the answer is:
avenge
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">requite</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for avenge that I've seen before include "Geneva (anag)" , "Exact reparation for a wrong" , "eg Nave (anag.)" , "Redress, vindicate" , "Get one's own back for" .)